Formed metal parts and in particular formed sheet-metal parts are manufactured in multi-component forming presses by deep drawing, restriking, folding, trimming, etc., involving different forming tools.
For the configuration of metal forming tools (for example, punches, dies, and blank holders), as well as for the configuration of metal forming processes (for example, tool forces, draw beads, lubrication, shape, and material for the sheet-metal blank), CAD/CAE (computer aided design/computer aided engineering) programs are utilized. These simulate and model, respectively, a metal forming process by means of finite elements on the basis of simulation parameters. Simulation parameters describe                the geometry or shape of the forming tools utilized in the metal-forming process,        process parameters or metal-forming parameters, such as the lubrication, processing forces, etc.        material parameters of the material being formed, such as thickness, rolling direction, physical characteristics etc.        
The simulation programs create, by numerical simulation, result values comprising a description of the geometry of a sheet-metal part after the forming process as well as the distribution of state variables, such as elongations and stresses in the formed sheet-metal part. They also may calculate, from the result values, values of certain characteristic variables, called performance variables, which express a quality of the formed sheet-metal part. Different types of performance variables and visual representations of the result values and performance variables can be computed and displayed in a post-simulation analysis. Correspondingly, further sets of parameters are used to control the numerical simulation itself (control parameters) and to control different types of post-simulation analysis (analysis parameters).
An important parameter in forming processes is the restraining force since it affects the flow of material in most areas of the part being formed. The restraining force is the force restraining the material of the part being pulled and stretched, from one or more areas of the part being held back by a blank holder, into the desired shape during the forming process. The restraining force may vary along the outer circumference of the part (and also at inner regions of the part being held by blank holders) and is influenced by a combination of the blank holder force(s), the arrangement of draw beads, and also by the shape of an addendum to the part, where such an addendum is arranged, etc. If the restraining force in a particular area of the part is too large, the material may thin out and tear, if it is too small, the material may be compressed (which may result in wrinkles or bad surface appearance). Depending on the geometry of the part, both of these undesired effects may arise in different areas of the part, so it may be necessary to find a middle value for the restraining force which minimizes the total risk of thinning and thickening. In order to do this, one may repeatedly perform a numerical simulation of a forming process, as described above, thereby varying the restraining force and other important parameters in order to find a set of parameters that gives a satisfactory result. However, this procedure is time-consuming due to the required computing power, and requires a lot of forming technology expertise.
There is a need to assist users with the choice of process parameters, in particular with the choice of restraining force.